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Lavender is a hardy plant that makes a great choice for hedging or ornamental shrubs. In fact, its aromatic nature actually deters a wide variety of pests, while attracting beneficial creatures like bees and butterflies. That said, there are a number of pests and diseases that can affect Lavender if you are not vigilant, so here are the most common Lavender problems and how to treat them.
Root Rot is caused by fungi found in soils, and it can be a common problem for many shrubs and hedges if they are planted in the wrong conditions. Lavender plants are likely to suffer from root rot if often overwatered, and if the soil drainage is particularly poor around them.
You can prevent this by ensuring you plant Lavender hedges and shrubs in full sun and well-drained soil. Lavender almost thrive on neglect! A Mediterranean plant, they require very little watering and should not be mulched as this retains moisture in the soil.
If root rot has already taken hold, try to catch it as early as possible, uprooting the lavender plant and cutting away the affected tissue. You can then re-plant it in a sunnier area of the garden.
You may notice that, at the base of your Lavender plant, the foliage is starting to turn grey – this is an early sign of Botrytis, a fungal disease that affects a range of garden plants in areas with high humidity and low airflow. The leaves will yellow, wilt and eventually die, harming the plant. You can prevent this by being careful not to overwater your Lavender, but otherwise removed all the infected leaves and spray fungicides to prevent the disease from spreading. This should help with stopping its progress.
This particular variation of leaf spot only attacks Lavender, another fungus that thrives in humid environments. This disease starts with tiny grey spots on the leaves that then spread and kill the foliage. While it is rarely fatal to Lavender, it can massively stunt growth by weakening it.
To prevent this, you need to keep the leaves as dry as possible, since water sitting on the leaves tends to encourage Septoria Leaf Spot. You can keep the Lavender plant dry by not crowding it, so air can circulate the whole plant, and occasionally pruning the interior branches to prevent the interior from becoming dense and humid. In rainy climates, ensure there is proper soil drainage.
If Septoria Leaf Spot has already infected your Lavender hedge, remove infected leaves to stop it from spreading further. Use organic fungicides like copper and neem oil to kill it.
Alfalfa Mosaic Disease is one of the two most harmful diseases that can affect Lavender shrubs and hedges. It is usually transmitted in one of two ways; either by aphids infesting the plant or because the gardener has not been sanitising their tools.
To prevent it, tools like pruning shears should be thoroughly sanitised, and the gardener can wear gloves to prevent spreading diseases through their touch as well. Weeding beds regularly and monitoring for pests like aphids are also key to prevention.
Unfortunately, if you suspect your plant has Alfalfa Mosaic Disease, you need to uproot it immediately – there is no cure for this disease, and it is highly contagious to surrounding plants. Make sure to carefully dispose of all infected plant matter, burning it if possible.
Finally Shab, a wind-spread fungal disease, is the other disease that is fatal to Lavender plants. It affects the green stems and woody branches of lavender plants, which will turn brown and start developing black spots.
While this disease is very rare in the UK, you cannot be complacent about prevention – make sure you only purchase Lavender seedlings from sources that offer certified disease-free stock, and don’t take cuttings from Lavender plants that show signs of disease. You may wish to consider researching which variations of Lavender are more resistant to Shab – French Lavender, for instance, is immune.
Once again, there is no cure, so collect any infected plants and destroy or dispose of them, while ensuring you wear gloves through every part of the process and sanitising them afterwards.
Both moles and voles can be a nuisance when it comes to Lavender plants – moles can uproot them by tunnelling underneath, and voles tend to eat roots and other plant material, so they can have a significant effect in no time.
Traps can be a very effective way of managing moles and voles, but you must ensure you are certain about which is causing the problem so you can buy the right kind of trap. Otherwise, adopting a cat or dog can be a simple way of deterring small mammals from disturbing your garden.
Fire ants can become a problem in the UK – if they form a nest underneath Lavender plants and tunnel around the roots, the plant will collapse and die. If you suspect fire ants may be the issue, simply lift the plant up – if fire ants pour out of the hole, they’re the source of the grief.
Thoroughly soaking the soil once it has dried out may discourage fire ants from building colonies there. Otherwise, try an insecticide specifically designed for fire ants, or for a more natural option you can try spreading diatomaceous earth on fire ant mounds and pathways.
Spittlebug Nymphs, also known as Froghoppers, are generally quite harmless – they affect a range of plants, also including rose and rosemary, producing a foam that encases plant stems. While it is generally harmless and you can often ignore spittlebugs, they can cause a bacterial disease called Xylella to infect the plant.
It is generally recommended that you do not try to remove spittlebugs if you see them, as they contribute to the biodiversity of your garden. While some suggest that you spray spittlebugs and “cuckoo spit” away with water, we do not necessarily recommend this either, as it can cause Septoria Leaf Spot. If you’re particularly concerned about a particular plant, you should remove the spittlebugs by hand.
Whiteflies are a species of sap-sucking insect that can sometimes be found on the underside of leaves. They feed on a range of plants and secrete a “honeydew” that can attract other pests like ants and lead to different kinds of mould affecting the Lavender plants.
There are not many pesticides to control whiteflies, but you can try different solutions like applying neem oil, planting companion plants to attract the predators, or removing them by hand. Thankfully, whitefly generally tend to avoid strong smelling plants so you are unlikely to see them on your Lavender!
You may notice that many of the common problems with Lavender plants have the same root causes. Monitoring for signs of disease and pests is very important, but you can keep your lavender happy and healthy by:
Following these guidelines will make the chances of the plant being ravaged by diseases and pests unlikely.
